Table 1.
Time constants for transitions of photocycle intermediates
| ChR2 Transitions | τ (H2O) | τ (D2O) | KIE of ChR2 | bR Transitions | KIE of bR |
|---|---|---|---|---|---|
| P1500 → P2390 | 8 μs (9.6 μs) | 14 μs (17 μs) | 1.8 (1.8) | L → M | 4.6–5.6 |
| P2390 → P3520 | 1.5 ms (2.3 ms) | 5 ms (7.0 ms) | 3.3 (3.0) | M → N | 1.7–1.8 |
| P3520 → P4480 | 6 ms (6.4 ms) | 19 ms (18 ms) | 3.2 (2.8) | N → O | 1.5–2.0 |
| P44 → ChR2a | 19 s | 49 s | 2.6 | O → bR | 1.5–2.0 |
Time constants were derived from lifetime distribution and multiexponential global fitting (in parentheses) of transient absorption changes of ChR2 at 360, 380, 440, 480, 520, and 540 nm after blue-light (450 nm) excitation. The sample was measured in H2O and D2O and the KIE is given by the ratio of the time constants. The KIEs characterizing the transitions of the various intermediate states of the bacteriorhodopsin (bR) photocycle were taken from the literature (35,41–44). Because the rise of the M intermediate in bR is multiexponential, the KIE for the formation of M is given for the component with the largest amplitude. The KIE of the recovery of ground-state ChR2 was determined by rapid-scan FTIR as described by Lórenz-Fonfría et al. (7).
Derived from multiexponential fitting of the rapid-scan FTIR spectroscopic data at 1242 cm−1.